There exist today numerous kinds of projectiles used by law enforcement agencies for hand guns carried by their personnel. Frequently, a design purpose of such projectiles is to maximize their ability to stop an assailant despite the projectiles' typically small caliber. These projectiles spread outward, or petal, when they penetrate a human target. This petalling maximizes the bodily damage to a would-be assailant and thereby maximizes the probability that such an assailant will be stopped.
Applicant's projectile is of the general class which petals upon penetration. However, applicant's projectile is unique because of features which control its rate of expansion relative to the rate of penetration. These features include a head separated into petalling elements by fins softer than the material of the head and a jacket whose longitudinal support of the petalling elements can be varied to change petalling rate. The configuration of the interface between the jacket wall and the petalling elements can also be varied to modifiy the relative rates of petalling and penetration.